This invention relates generally to fiber optic angular rate sensors using square wave phase modulation. More particularly, this invention relates to an angular rate sensor of the type described having reduced output signal distortion for improved performance. Still more particularly, this invention relates to an angular rate sensor using square wave phase modulation and including means for suppressing transient jumps or spikes which degrade and distort the angular rate sensor output signal, without modifying the signal processing configuration of the sensor.
Transient jumps or spikes in the output signal of an angular rate sensor are inherent in both open and closed loop angular rate sensors using square wave phase modulation. These spikes are undesirable since they contain no useful angular rate information and serve only to degrade or distort the useable portion of the output signal.
Prior to the present invention, attempts have been made to minimize the effect of these spikes by minimizing the rise and fall times of a bias signal provided in the angular rate sensor arrangement, or by electronically filtering the angular rate sensor output signal via a low pass filter. Both of these arrangements have significant disadvantages.
Minimizing the rise and fall times of a bias signal requires a bias signal generator having increased power consumption and bandwidth. While this arrangement reduces the duration of the spike, the spike is not entirely eliminated. Additionally, increased bandwidth results in an undesirable increased susceptibility to modulation noise.
Filtering the output signal reduces the amplitude of the spike but the amount of filtering which can be applied is limited since the energy in the spike spreads out to degrade or distort the output signal. Additionally, in a closed loop fiber optic angular rate sensor, the generated signal is usually highly amplified to increase the sensitivity of error signal detection. The presence of a spike results in a signal which is far beyond the dynamic range of amplifiers providing the high amplification so as to overload the amplifiers. Additional signal distortion occurs as the amplifiers recover from this overload.
Accordingly, the present invention provides an arrangement for suppressing spikes in the angular rate sensor output signal for improving angular rate sensor performance characteristics including random walk and bias stability. Additionally, scale factor linearity and scale factor stability are also improved.